In many industrial applications, the tightening of threaded fasteners to a specific degree or torque is of critical importance. In the assembly of automobiles or aircraft, it is imperative that nuts, bolts, screws, lugs, and the like (which, for brevity, will all be referred to as “bolts”) are sufficiently tightened to ensure that the resulting assembly functions properly not only at initial use, but over the long term. Over-tightening, however, may strip the threads or cause vibrational problems in the assembly.
It has long been known to use torque wrenches to tighten bolts. Such wrenches not only enable the user to rotate and tighten bolts, but also provide the user with a visual, audible, or tactile indication of the amount of torque that has been applied. Some known arrangements include slipper type, beam type, deflecting beam type, click type, and electronic strain gauge type indicators. The click type torque indicator is frequently used in wrenches designed for use in automotive applications and often includes a calibrated clutch mechanism disposed in a handle, or lever arm, of the wrench. When a user has applied the pre-selected torque force, the clutch mechanism clicks, providing the user with both an audible sensation and a tactile sensation that the pre-selected torque force has been applied. U.S. Pat. No. 4,655,104 to Blattner describes one type of torque indicator in detail, and that disclosure is incorporated into this disclosure by reference.
The head of a torque wrench can be configured as a ratchet wrench. However, the amount of play that is provided in some ratchet wrenches can affect the accuracy of a torque indictor, so not all ratchet assemblies are always appropriate for use in torque wrenches.
Ratchet wrenches have a ratchet assembly that engages and drives the bolt when the wrench is rotated in one rotational direction and disengages when the wrench is rotated in the opposite direction, enabling the user to move the wrench without reversing the prior movement, and thus enabling a user to avoid the need to remove and reposition the wrench when further rotation in one direction becomes blocked or inconvenient. The type of slide gear ratchet assembly seen in U.S. Pat. No. 6,341,543 has a ratchet wheel, a slide gear with sets of opposed teeth, and a ball and spring assembly that releasably biases the teeth on the push bar against teeth on the ratchet wheel. A user can selectively switch the wrench so that one or the other of the sets of opposed teeth on the push bar engage the teeth on the ratchet, thus configuring the ratchet assembly so that it either drives when rotated in a clockwise direction and releases when rotated in a counterclockwise direction, or vice versa.
To enable a user to readily shift between one mode of operation and the other, the slide gear on the prior ratchet wrench is slidably disposed within a bore that extends laterally through the head. The slide gear is wider than the head, and one lateral end projects out one side of the head in one mode of operation, and the other lateral end projects out the other side of the head in the other mode of operation. The user switches the ratchet assembly between modes of operation by pressing the projecting end of the slide gear into the bore. This motion shifts one part of the slide gear out of engagement with the ratchet wheel and another part of the slide gear into engagement with another part of the ratchet wheel, and pushes the other end of the slide gear out of the other side of the head.
While the projection of the ends of the slide gear makes it easy for a user to shift the wrench between the two modes of operation, it also creates problems. First, the arrangement of the lateral bore requires multiple set-ups on a computer-controlled vertical mill, making it more time-consuming to machine the head of the wrench. Second, the projecting end of the slide gear creates a risk of unintentional shifts of the wrench between modes and operations. Because the ratchet wrench creates a single-ended torque couple, workers place the palm of one hand over the head of a wrench to counter the side force, and that hand can apply sufficient force on the projecting end of the slide gear to cause it to shift out of position. Third, the exposure of the bore and the slide gear to the environment creates a risk that dirt, metal dust, or other materials will enter between the two moving parts and ultimately damage the wrench.
The slide gear on the prior wrench has a rounded profile that enables an easier fit in the lateral bore and may provide some tolerance for debris in the slideway. However, axial rocking of the slide gear in the bore can lead to point contact between the teeth on the ratchet wheel and the teeth on the slide gear, and such contact significantly increases the stresses on the teeth and can lead to quicker breakage.